Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this specification.
Physical beneficiation of low grade ores to yield a higher grade product as feedstock for further downstream processing is a key component of many metallurgical operations. The format of the overall physical beneficiation process, which may consist of more than one individual but integrated unit steps, is typically designed to maximise a number of positive technical and economic outcomes when the processing flowsheet is considered in detail as a whole.
Regardless of the mineralogical complexity and number of target minerals of an ore, the format of the physical beneficiation process is primarily concerned with achieving the optimum balance between the grade of the beneficiation product(s) and the overall recovery of the target mineral(s) into the beneficiation product(s). This balance is especially relevant for lower grade and more complex ores, and more especially ores that contain one or more target minerals.
The capital and operating costs associated with the downstream processing of a high grade concentrate are considerably more advantageous than those applicable to treating a higher volume of a lower grade concentrate to achieve the same overall recovery (mass) of target mineral(s) on completion of the downstream circuit. The capital and operating costs must also take into account that the recovery of target mineral(s) into a higher grade concentrate is typically lower than that attained with a lower grade concentrate. That is, a certain higher percentage of the target mineral(s) typically may not be recovered into the higher grade concentrate because of, for example, restricted mineral phase liberation at the selected-processing particle size.
Almost without exception, uranium ores and concentrates are leached under either alkaline or acidic conditions, the choice of leachant being a direct consequence of the uranium mineralogy itself, and more particularly the mineralogy of the matrix of gangue minerals. For some run-of-mine uranium ores the grade and mineralogy are such that pre-leach treatment is limited to crushing and agglomeration for heap leaching, or crushing and wet grinding for conventional tank leaching. Radiometric sorting may be applied if appropriate.
For lower grade uranium ore, the feedstock to the downstream leaching circuit will often be produced by a combination of physical techniques such as heavy media separation (gravity) and flotation. For example, U.S. Pat. No. 2,847,629, U.S. Pat. No. 2,697,518, U.S. Pat. No. 3,964,997, U.S. Pat. No. 4,070,276 and WO 2011/161650 describe procedures for recovering uranium concentrates by froth flotation procedures of varying complexity. The feedstocks for the processes described in these documents range from run-of-mine ores, to tailings, to sulphide (pyrite) concentrates. The complexity of the froth flotation procedures is a reflection of the mineralogical complexity of the feedstock and the level of concentration (upgrading or mass pull) required due to the large volume and low concentration of uranium in the feedstock. Thus, for example, WO 2011/161650 describes a method in which the flotation collector is added incrementally in 3-6 separate steps. This adds considerably to the physical size and complexity of the froth flotation circuit. As a consequence, the processing of lower grade ores by methods known in the art is sub-economic.
There is therefore a need for commercially viable processes for upgrading the concentration of uranium in ores derived from low grade uranium ore.